The intestinal apparatus is affected by many inflammatory diseases generally capped as inflammatory bowel diseases. In particular, Crohn's disease is a severe chronic inflammatory disease affecting various levels of the digestive tract, from the mouth to the anus, particularly it can be observed in the last portion of the small intestine, either the ileum, the colon or both and sometimes in the mucous membrane of the colon and in the anal region as well. In the interested intestinal part, inflammation, swelling and ulceration occur in the whole intestinal wall causing stenosis, bleeding ulcers and pain, while the non-affected tissue portions appear normal. Crohn's disease exhibits alternate periods of inflammatory symptoms of variable gravity with symptoms such as: diarrhoea, abdominal pain, weight loss often accompanied by rhagades or peri-rectal fistulas. From two-thirds to three-quarters of patients with Crohn's disease require surgery at some point in their lives. Surgery is used either to relieve symptoms that do not respond to medical therapy or to correct complications such as blockage, perforation, abscess, or bleeding in the intestine.
The role of the intestinal bacterial flora in the etiopathogenesis of the intestinal inflammatory diseases and in particular in Crohn's disease is evidenced by, for example, the frequency of localization to areas with high bacteria concentrations, see Jannowitz, H. D., in Inflamm. Bowel Dis., 1998, 44, 29-39; the deviation of the faecal flow determines remission of the endoscopic damages which reappear again at restoration of the canalisation, see Rutgeerts, P., in Lancet, 1991, 338, 771-774; experimental models, e.g., knock-out mouse for the IL-10 gene or others, show that spontaneous colitis does not develop if a “germ-free” condition is maintained, see Blumberg R. S., in Curr. Opin. Immunol., 1999, 11(6), 648-56; inflammation of intestinal mucous membrane develops after the contact with faecal material, see Harper P. H., in Gut 1985, 26(3), 279-84; after surgical “curative” therapy consisting of ileocolic anastomosis, antibiotic treatment delays the development of both endoscopic and clinic relapses, see Cameron J. L. in Ann. Surg., 1992, 215, 546-52; and the presence of fistulae or abscess-sacs points out further the bacterial contribution to the disease development.
Crohn's disease has previously been treated with drugs that are able to decrease or control the inflammation, e.g., cortisones, salazopirine, mesalazine, immunosupressants, specific chemotherapeutics, antibiotics and protein inhibitors of the actions of the Tumor Necrosis Factor (TNF). During the treatment of the acute phase of the inflammatory bowel disease, stronger treatments are often necessary to ensure parenteral alimentation, to reconstitute the loss of proteins, liquids and salts, to permit the intestine to rest to facilitate the cicatrisation of ulcers. The purpose of the therapy is to decrease the frequency of the reappearance of symptoms and to reduce the seriousness acute episodes when they appear. However, with current therapies, acute episodes respond in about 50-70% of the cases, but relapses occur in 80% of the patients.
Antibiotics are usually used to decrease the growth of the luminal bacteria; to decrease the inflammatory state sustained as a result of the bacterial growth; to reduce symptoms of the acute phase of the disease, e.g., diarrhoea, intestinal pain and meteorism; and to prevent and to cure septic complications, e.g., abscesses, fistulas and toxic state.
The most frequently used antibiotics are systemically absorbed, for example, metronidazole (active against some parasites along with many anaerobic bacteria) and ciprofloxacin (active against such bacteria as E. Coli and aerobic enterobacteriace). Metronidrazol has been used at a dose of 10-20 mg/kg/day for 4 months (Sunterland, L. Gut, 199132, 1071-5), while ciprofloxacin has been used at a dose of 1000 mg/day for 6 weeks (Colombel J. F. in Am. J. Gastoenterol., 1999, 94, 674-8), while Prantera in Am. J. Gastoenterol., 1996, 91, 328-32, adopted the combination of the two antibiotics using metronidazole at the dose of 1000 mg/day and ciprofloxacin at the dose of 1000 mg/day for 12 weeks. The high systemic bioavailability of these antibiotics is at the root of their high incidence of side effects registered in long-term therapies, which negatively impacts their use. The incidence of side effects in the use of metronidazole ranges from 10% to 20%, depending on the dose and the treatment duration. The most frequent side-effects include metallic taste, gastric intolerance, nausea, glossitis, cephalea, vertigo, ataxia, convulsion and neurotoxicity. Peripheral neuropathy has been recorded in 50-85% of the long-term treated patients, which may regresses only after several months of therapeutic interruption. The percentage of side effects described in ciprofloxacin studies is variable and depends in part on the dosage and the duration of the treatment. The most frequent of the side effects are of gastrointestinal origin, but an increase of the transaminase and skin reactions have also been frequently described. Thus, there is a need in the art for a long-term treatment option for inflammatory diseases of the digestive tract, e.g., gastro enteric pathologies.
It is advantageous for pharmaceutical preparation used for treating inflammatory bowel diseases (e.g., gastro enteric pathologies) that are based on antibiotics to have one of more of the following characteristics: intestinal level activity, low absorption, bacteria level control in the intestinal lumen, wide spectrum of actions against the microbes (e.g., intestinal Gram-positive, Gram-negative, aerobic and anaerobic components), possibility of long term therapy without side effects, ease of administration to facilitate compliance even with the potential of high dosage necessity, e.g., long-term dosing and/or multiple dosing per day.
An antibiotic possessing several of these characteristics is rifaximin (INN; see The Merck Index, XIII Ed., 8304), which is characterized by a wide spectrum of action against many Gram-positive and Gram-negative bacteria, including aerobic and anaerobic bacteria. Bioavailability studies in healthy volunteers have shown that, when given orally, less than 1% of rifaximin is absorbed and it concentrates in the intestinal lumen and in the faecesas described herein (Descombe J J. et al. Pharmacokinetic study of rifaximin after oral administration in healthy volunteers. Int J Clin Pharmacol Res, 14 (2), 5′-56, (1994)). The absence of rifaximin absorption has been confirmed in patients affected by chronic bowel disease, (see Rizzello, Eur. J. Clin. Pharmacol. (1998) 54, 91-93). Moreover, the low absorption profile of rifaximin reduces the incidence of side effects and the unwanted risk of pharmacological interactions. Thus, rifaximin may be considered useful in the therapy of inflammatory chronic bowel disease and particularly in Crohn's disease. The potential efficacy of rifaximin in chronic inflammatory bowel diseases has been confirmed, see Gionchetti, P., Dig. Dis. Sci., 1999, 44, 1220-1, who hypothesized the use of rifaximin in patients with moderate or severe ulcerative colitis refractory to steroid-treatment.
Rifaximin has been described in Italian Patent IT 1154655 (1980) and EP 0161534 (1985), both of which are incorporated herein by reference in their entirety for all purposes. EP 016153 discloses a process for rifaximin production using rifamycin O as the starting material (The Merck Index, XIII Ed., 8301).
Guidance for rifaximin crystallisation and drying are described in Italian Patent Application No. MI2003A002144 (2003), in European Patent Application No. EP 1557421 (2003); in U.S. patent application Ser. No. 10/728,090 (2003) in PCT Patent Application No WO2005/044823; all of which are incorporated herein by reference in their entirety for all purposes. The experimental conditions described in these patents allow yielding polymorphic forms of rifaximin named Form α, Form β, Form γ, Form δ and Form ε, respectively.
Rifaximin is approved in certain countries for the treatment of pathologies whose etiology is in part or totally due to intestinal acute and chronic infections sustained by Gram-positive and Gram-negative bacteria, with diarrhea syndromes, altered intestinal microbial flora, summer diarrhoea-like episodes, traveler's diarrhoea and enterocolitis; pre- and post-surgery prophylaxis of the infective complications in gastro intestinal surgery; and hyperammonaemia therapy as coadjutant. Rifaximin is currently marketed as tablets or capsules at the dosage of 100 mg and 200 mg, in a ready to use preparation for children, or as ointment for the treatment of topical infections.
Studies on commercially available samples, particularly 200 mg tablets, have shown a potential usefulness of rifaximin in the prevention of the relapse of Crohn's disease after endoscopic resection. However, the absence of a placebo group in the clinical trial does not allow to draw confident conclusions, see Rizzello, Gut., 2000, 47, Supp. 3, A12. However, the suggested posology the use of the rifaximin 200 mg tablets has to be considered sub optimal due to the need up to six tablets a day for three months, resulting in a poor patient compliance. The 200 mg tablets of rifaximin have also been used in the treatment of Crohn's disease with dosages of 600 mg/day for 16 weeks as described by Shafran, I., Am. J. Gastroenterol., 2003, 98 (Suppl.) S-250.
Thus, there is a need in-the-art for a rifaximin pharmaceutical formulation for the treatment of infections specifically located in the intestinal tract. Previous formulations, after administration, are released and spread between the stomach and the intestine. Thus, when the rifaximin finally reaches the intestinal tract, the concentration is too low resulting in the need for increasing dosages. To maximize the therapeutic efficacy of rifaximin in the treatment of bowel diseases, new pharmaceutical formulations are provided herein and include, for example, rifaximin microgranules coated with a gastroresistant film which dissolves releasing the antibiotic only in the intestinal tract. This novel formulation maximizes contact between the active ingredient and the intestinal mucous due, in part, to the high superficial area of the microgranules. The novel formulations also allow for ease of high and low dose administration, for example, in paediatric use.
The novel gastroresistant rifaximin formulations takes advantage form the pH difference between the gastric environment (e.g., values from about 1.5 to about 4.0, depending on the state of fast or in presence of meal) and the intestinal lumen (e.g., values from 5.0 to about 7.5, depending of the tracts considered).
The novel forms also utilize the polymorphic forms of rifaximin.
The coating of pharmaceutical microgranules with gastroresistant film is a technique known by many years in the pharmaceutical field. It is generally performed in two steps: granulation and coating. Nevertheless, many active substances, including rifaximin, are characterized by a very fine particle size, for example, in case of rifaximin approximately 50% of the particles has a particle diameter between 10 μm and 40 μm. In such condition it is very difficult using conventional systems like fluid bed coating or pan technology. Very often agglomeration occurs or random blend of coated and uncoated particles is commonly obtained.
We have found, and this is an object of the invention, that it is possible to obtain enteric-coated microgranules of rifaximin by applying the fluid bed technology, which surprisingly allows in one step and at the same time to perform the wet-granulation of the powder and the coating of the formed microgranules with a polymer resistant to the gastric environment, commonly called enteric coating. With this approach the chief disadvantages of the wet-granulation and microgranule coating, which are in separate steps involved as well as the time and labour necessary to carry out the entire procedure, especially on the large scale, are minimised. This result comes from a combination between the rifaximin properties and a proper balancing the quantity of rifaximin, of enteric polymer, of plasticiser, and process parameters.
The efficiency of this technology in providing a complete coating layer around rifaximin is demonstrated by SEM microscopy as reported in FIGS. 1a (Scanning electron microscopy of rifaximin gastroresistant microgranules) and 1b (Scanning electron microscopy of single granule of rifaximin gastroresistant microgranules), where it is clearly show that rifaximin is fully coated by the enteric polymer. The particles sizes are quite homogeneous without large clots or very fine powder. If present, one or both of these aspects would have negative impact in any further medicinal preparation.
As confirmation of the completeness of the coating, the dissolution profile of the gastroresistant microgranules of rifaximin shows that rifaximin is completely retained at low pH and released at pH higher than 5.0, as reported in FIG. 2 (Dissolution profiles).
In order to maximize the release of the active ingredient near the intestinal mucous membrane it has been utilized high pH difference between the gastric environment, values from 1.5 to 4.0, depending on the state of fast or in presence of meal and the intestinal lumen, values from 5.0 to 7.5 depending of the tracts considered. For this purpose, enteric polymeric materials having the property to solubilize at pH values between 5.0 and 7.5 have been used, to include: methacrylic acid copolymers with an acrylic or methacrylic ester like methacrylic acid ethylacrylate copolymer (1:1) and methacrylic acid methylmethacrylate copolymer (1:2), polyvinyl acetate phthalate, hydroxypropyl cellulose acetate phthalate and cellulose acetate phthalate, products available on the market for example with the trademarks KOLLICOAT®, EUDRAGIT®, AQUATERIC®, AQOAT®.
The application of these gastroresistant films to rifaximin powder or granules is performed with conventional apparatus for fluid-bed coating technology. The film coating, dissolved in organic solvents or suspended in water, is applied by spraying on powders or granules maintained in suspension with air in fluid bed systems. The most used organic solvents are: methylene chloride, methyl alcohol, isopropyl alcohol, acetone, tri-ethyl acetate and ethyl alcohol. Alternatively, the polymeric gastroresistant material can be applied suspended in water. This technique is preferable because it doesn't need the use of solvents and so it avoids the toxicological and safety related problems.
Other excipients with anti-agglomerative properties, like talc; plasticizing properties, like acetilated glycerides, diethylphthalate, propylene glycol and polyethylene glycol; surfactants like polysorbate and polyoxyethylenate esthers, anti-foam as well as anti-sticking agents can be added together with the polymeric material.
The successful application of the above mentioned technology to the coating of rifaximin powder is remarkable because it is not in the state-of-art of fluid-bed technology to spray the enteric polymer directly on the active ingredient without any preliminary treatment like granulation or layering the active ingredient on inert particles. Indeed, several drawbacks could occur without any powder pre-treatment such as large clamp formation, large range of particle diameter, inhomogeneous composition of microgranules, no uniform coating layer. The occurrence of some of these drawbacks is common with rifaximin, the powder of which is composed by a fine particles, and is extremely hydrophobic, electrostatic, hygroscopic and difficult to be mixed with common excipients in powder. Moreover it has a predisposition to segregate not allowing homogenous mixture. In presence of such unfavourable characteristics to get coated rifaximin would required the use of more than one step and a large quantity of excipients, which would limit the pharmaceutical strengths of human dosage.
As further advantage of the present invention, the gastroresistant microgranules of rifaximin prepared on the basis of the described technology of the present invention can directly be used to fill capsules or can be mixed with excipients and sweetener enhancers giving the possibility of an aqueous suspension administration.
In addiction and more remarkably the gastroresistant microgranules of rifaximin can also be directly used for tablet preparation through direct compression technology by adding conventional vehicles or carriers. As additional advantage, the tablets can be scored in order to modulate the dose strength or to be crushed to facilitate the ingestion without losing the gastroresistant property of the microgranules.
All these opportunities confer significant value to the technology described in the present invention to prepare gastroresistant microgranules of rifaximin, making it suitable for a wide modulation of dosages and pharmaceutical forms.
In conclusion, the present invention shows, with respect to other marketed rifaximin preparations, remarkable improvements that can be summarized on the possibility to manufacture in only one steps gastroresistant microgranules of rifaximin, which remain insoluble in the stomach (e.g., at a range of pH between about 1.5 and about 4.0) and soluble in the intestine (e.g., at higher pH, for example between about 5.5 and about 7.5), to administer high dose, targeting the maximum release of the active ingredient in the intestine and at the same time maximizing its contact with the intestinal mucous membrane because of the high superficial area of the microgranules.